Drying protocol does not alter plant δ¹³C and δ¹⁵N: a baseline survey for ecological studies

Drying protocols might alter the isotopic signatures of plant samples given that high temperatures can volatilize various organic compounds or delay the halting of physiological processes at lower drying temperatures. We thus evaluated the effect of four drying protocols on the carbon and nitrogen isotopic signatures for 23 species of plants. In particular, leaves were either freeze-dried, placed in a herbarium drying stove (ca. 50°C), in a gravity convection oven (80°C), or microwaved (900 W) in 2-minute pulses, until constant weight. For each species, neither treatment led to significantly different δ¹³C values, which ranged from -31.7 to -12.4‰. The δ¹⁵N values of 21 of the species considered were not affected by the drying protocols, ranging from -11.6 to -8.8‰. For Tillandsia makoyana, significant differences were observed between the freeze dried and the microwaved samples and between the freeze dried samples and those dried at 50°C for Macroptilium gibbosifolium.